The converse also holds; that is, given \(\psi \)  as in the Lévy-Khintchine
representation (REF ), there exists a Lévy process \(X=\lbrace X_t\rbrace _{t\ge 0}\)  with the characteristic exponent \(\psi \)  .
Details about Lévy processes can be found in
[1]}, [2]} .
